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Why Malaria Kills
by Anil Patel


Introduction to "When Politics Kills: Malaria and the DDT Story", to be published by the Liberty Institute in Delhi, India, on
March 7, 2001

In "When Politics Kills: Malaria and the DDT Story", authors Richard Tren and Roger Bate have done a very useful job. They have dared to speak out: to espouse the cause of DDT, the dirtiest of the "Dirty Dozen", in man's war against malaria.

In these days of "correct politics" when the DDT has become synonym with environmental pollution and degradation, it is not easy to say what they have said. Independent of environmental considerations, the non-use of the DDT in the fight against malaria had seemed to be a settled issue because of the epidemiological reasons. Tren-Bates have brought in the focus the environmental angle and argued cogently to reconsider the whole gamut of issues.

We have forgotten the dread malaria used to hold in India in the 19th century and the beginning of the 20th century. Seventy Five million people were down with malaria, which would be about one in five or perhaps more of the population then. A little less than a million were dying every year. One reads the fearful accounts of the villages after villages being laid waste by malaria in Sharat Chandra Chattopadhyay's stories. Vast tracts of lands were uninhabitable because of malaria. The economic cost and the resultant human misery were staggering. For the most part of the written history, man was helpless against the might of anopheles mosquito and malaria parasite. The things took a turn for better in 1898 when Sir Ronald Ross, an army doctor dissecting thousands of mosquitoes in his tiny lab in Madras (now Chennai), demonstrated developing malaria parasite in the body of female anophelene. The complex life cycle of malaria parasite in the vertebrate human host and invertebrate mosquito was elegantly displayed for the first time by Ross. This opened up a vast field of control of malaria, unimaginable until then.

After Ross, malaria became intricately linked to mosquito. I am tempted to quote L. J. Bruce- Chwatt, a close associate and successor to Professor Macdonald, one of the most outstanding founding fathers of epidemiology of malaria:

"In the series of factors of the epidemiology of malaria, some of the most important relate to the vector (mosquito). The proportion of the population of mosquitoes which live long enough for the development of malaria parasites in them depends on the mortality to which they are exposed. Next comes the question of how long the mosquitoes may be expected to survive before they transmit the infection to another person. The proportion of survivors of an Anopheles population decreases exponentially with time and this has an important bearing on the probability of transmission. The concept of the expectation of life of mosquitoes, which depends on the environmental conditions, runs like a red thread through the complicated weave of the pattern of epidemiology of malaria."

Professor Macdonald worked out the crucial factor of mosquito longevity that constitutes the red thread of a pattern of malaria epidemiology. Based on the mathematical model of malaria epidemiology, he worked out a theory of equilibrium of malaria in different situations. He argued that the various determinants of malaria cannot be given the same weightage. The longevity of adult mosquito and the mosquito's preference or lack of it for human blood meal are the most crucial determinants of transmission of malaria in human populations. They determine the extent of stability of malaria in a given population of an area. His model showed convincingly why malaria was deeply entrenched and stable in the large parts of continent of Africa and in some parts of East Asia. The same model could explain why malaria was unstable in India, China and vast areas of Europe. About the time when Macdonald's working out of the malaria epidemiology was reaching its peak, it was discovered in Greece and other Southern States of Europe that intensive indoor spraying of the DDT for years to eradicate mosquitoes had wiped out malaria from the region, but the mosquitoes returned.

There was, thus, a great paradox of anophelism without malaria created. The malarialogists were perplexed, but Macdonald's model lucidly explained this. By this time, vector mosquitoes had started developing resistance to the most popular insecticide DDT, in many areas. Macdonald argued that without losing time the eradication of malaria must be attempted. His objective was deep and specific; to cut all the transmission links between mosquitoes and humans for long enough time by focusing on the longevity factor of mosquitoes. This would ensure the natural disappearance of parasites in the human population without any chance of being transmitted to another human being through mosquitoes. Residual indoor insecticide spray was the keystone of the whole strategy of eradication.

He and his colleague, G. Davidson worked out meticulously the details of the insecticide formulations, the doses and countless, tiny, but crucial details of the indoor spraying of insecticide. Mosquitoes after biting human being with some exceptions have to rest on the indoor surface treated with the DDT. The DDT may not instantly kill the mosquitoes but would shorten the life of the mosquitoes to an extent, which will not be enough for the sexual form of malaria parasites in the stomach of the mosquitoes to develop into infective asexual forms of parasite. The long life of the DDT on the surface would ensure that such interruptions of transmission continued for a long time.

No other determinants of the malaria transmission were as potent as the longevity after biting the human being and no other was so amenable to human actions as this one. This was the crux. Macdonald had shown the weakest link of the chain of transmission. Based on this deep insight, the eradication program of malaria was launched all over the world except Africa, where the social and political structures were considered weak, and in some parts of the Middle East. Europe and America had already achieved the eradication of malaria.

This was a momentous campaign. Never before, the mankind had embarked on such a scale against any killer disease. Fred Soper in America in 1930s had shown the way through a massive campaign against Aedes Egypti a vector mosquito which was spreading a deadly disease of yellow fever in the Central America. Yellow fever had to beat a retreat. Then he mounted a huge campaign against one of the deadliest vector mosquitoes of malaria, Anopheles Gambiae, when the species invaded Brazil from Africa. He repeated the performance against the Anopheles Gambiae when it first invaded Egypt. But for Soper's heroic battle against vector mosquitoes using all the tools, including insecticides at his disposal, the deadly disease would have entrenched itself in Brazil and Egypt like it did in a large part of African continent. (This is all true, but it must be noted that whereas Fred Soper wanted to eliminate invading mosquitoes, MacDonald was aiming at eradication of parastites, not vector mosquitoes.)

The eradication campaign of malaria in India almost worked a miracle. The incidence of malaria fell from the dizzy height of 75 million cases per annum to merely 50,000 cases per annum. By any standard, result and impact was spectacular. The whole generation of doctors, like me, grew up in the decade, when not a single case of malaria in the teaching hospitals was seen.

MacDonald had said that it was not enough to think, like mosquito, to deal with malaria, it was necessary to think like Soper, who, he said, had argued that to eradicate infection is to remove both branches and roots. Eliminate the branches first, then identify the roots small, hidden foci of infection where the infection is ceaselessly transmitting and eliminate those foci.

The eradication campaign in its attack phase eliminated the branches, but when it came to identification and elimination of small foci of incessant transmission, that is the consolidation phase, India stumbled badly. The DDT resistance was blamed for the failure of consolidation phase. But surely, this is not the full explanation. Most to blame is the complacency of the administration, lack of foresight and political will to go after the disease, when it was so down and low. Macdonald, of course, was not dogmatic about the indoor insecticide spray as the only tool of eradication campaign. Having worked long years in Africa and India, he was fully aware and sensitive to local situations, limitations and possibilities. He patiently argued that the key was to continually disrupt the chains of transmission in the community. He accepted that in certain areas mass drug administration could be the best way to disrupt the chains. He also understood that in many societies there were difficulties and problems, which were not amenable to standard or even a quick solution. His was the plea to remember the larger perspective of global eradication in which certain difficulties, essentially local, biological or social, had to be understood and dealt with. Serious setback to eradication in India, at least in retrospect, was inevitable, because the concept of eradication was not adequately grasped and accepted by the decision-makers.

Because of the biological intricacies of man, mosquito and the malaria parasite in Africa, malaria is so stable and deeply entrenched that the eradication is extremely difficult, if not impossible. Again, MacDonald was the first to see this, explain this and think about the possible strategies in Africa. There were attempts to reduce transmission, using Macdonald's model. The results were not satisfactory, let alone spectacular, as they were in India and elsewhere. Indoor, residual insecticide spraying had limitations in Africa, mainly because of the vectorial capacity of A. Gambiae and A. Funestus.

Malaria campaign driven by insecticide spraying was stalled. There was a kind of a backlash to the eradication strategy. The critics said that the model was not good enough to change the situation in Africa. They also said that the eradication strategy in India ignored socio-economic factors and instead of aligning with and encouraging decentralized health-services deep in rural area, it adopted a vertical approach, i.e. it created its own structure, including command from top to bottom and sought to eradicate one disease while ignoring the genesis and rooting of all the major illnesses afflicting the poor people. I was also swayed by this criticism. In those days, I also accepted the line that insecticide spraying was not a right strategy.

After a lapse of nearly 25 years, I am not as sure of that as I was then. I have observed the unfolding scenario from very close quarters. There is no network of efficient health services dealing with deep-rooted killer or maiming diseases, such as malaria, tuberculosis, gastro entritis, pneumonias, STDs, etc. A large state network of health services in the villages is rudderless, non-functional and riddled with corruption. An unscrupulous and ignorant network of quacks and even qualified but irrational practitioners have come to occupy the vacuum. The state hardly cares and notices the serious development, let alone creating credible network of health service.

Meanwhile, malaria resurgence is in full swing. From nearly extinct in mid '60s, it is now climbing up the curve of incidence. According to one estimate, there are now 25 to 30 million cases of malaria every year in India, not very far from the historic high of 75 million cases. Falciparum malaria (killer malaria) was almost unknown in the state of Gujarat only a few decades ago. Now it is estimated that in such big urban pockets as Surat it could be 35% or even more of the total cases of malaria. The chloroquine resistance is spreading like a wild fire. Its heat can be felt as deep as 200 kms in the tribal hinterland.

Urban malaria has assumed a dangerous proportion and the unnerving parasites resistant to cheap and effective chloroquine is spreading deep into the rural areas through migrant workers. There is no comprehension of the problem at the government level. Major epidemics of malaria described graphically by Macdonald and his contemporaries are now lurking in the background. The intrinsic instability of malaria and such an explosive background can easily trigger a devastating epidemic anywhere, anytime in India. Outside Africa, India now has the largest number of malaria cases in the world. It is in this sobering context, I am forced to revise my earlier criticism of the eradication strategy based on insecticide spraying. Even in those days, Macdonald had acknowledged that his model of eradication was deterministic. It took only averages into account, which might not be an accurate account of many foci of transmission named as Spatial Units of Transmission (SUT).

In such SUTs, better assessment could be made by using probabilistic models, which might require much longer spray of the DDT than envisaged in general attack phase of 2 to 3 years. There were those who argued that if such SUTs could have been identified and dealt with appropriately, the story of eradication could have been different.

Leaving behind the ifs and buts of history, we turn to the actual happenings, which Tren and Bate have brought into focus. After eradication campaign had received a set back, there was a reassessment of the situation. From what Tren-Bate describe, the eradication strategy of focusing on "the red thread of mosquito longevity after the blood meal" came to be identified as exclusive vector control method. This is, however, not the correct interpretation. Macdonald in fact was first to understand and explain the fundamental fact that indigenously entrenched vector mosquito cannot possible be eradicated, but malaria parasites can be. The phrase 'anophilism without malaria' brings out this situation pithily.

WHO came up with a new strategy to deal with a new situation: the Roll Back Malaria (RBM) Program. This program moved away from "vector control" to rely heavily on diagnosis, drug therapy and other measures like impregnated mosquito nets. On the face of it, it seemed a sensible thing to do.

Tren-Bate have given a fascinating historical account of two strands of approaches to malaria, that have persisted through the whole of the 20th century. The first relies on the drug therapy, hoping to eliminate parasite pool from the human population to achieve eradication. The second has tried to eliminate vector mosquito to achieve eradication.

Ronald Ross discovered the life cycle of parasite in the female mosquito in 1898. Ross and following him Fred Soper became strong advocates of mosquitoes' elimination, to eliminate malaria parasites. The strategy was to identify and remove breeding places and to use pyrethrum spray to control adult mosquitoes.

Another school of thought in Italy founded by a social reformer Angelo Celli, however, focussed on the malaria parasites in the human population and advocated strongly quinine-based malaria control.

The two schools existed alongside each other and competed against each other. Neither approach was a great success in the fight against malaria before the advent of DDT. DDT, which was first introduced to control insect pests in farms in 1930, was used in the Second World War to control the body lice to control typhus. Soon after the war, it was used to control malaria, with a dramatic success. DDT soon became a chief weapon to control the vector mosquitoes, which was the most effective way to stop transmission of the parasites. As discussed above, in the Macdonald inspired eradication strategy also, DDT occupied a strategic position, but its role varied in different phases of eradication and the use of drugs like chloroquine and primaquine was integral to the whole strategy, because the aim of the strategy was not to eradicate mosquito but the parasite from the human population.

The move from the residual insecticide to the use of the drugs and nets is, however, not a simple swing of pendulum from one end to another end, following an apparent failure of the eradication strategy. As delineated carefully by Tren and Bate, soon after the global campaign against malaria was launched after the end of Second World War, some neo-Malthusians like Vogt had started raising their protest, arguing that it was unkind to prevent malaria deaths because survivors could die of slow starvation. They made their favorite assumption that the resources were limited and surviving humans are mere consumers and not producers of the resources! Echoing the modern day environmentalists, they also argued that developing technologies "... may even wipe out various forms of the disease entirely, but then another difficulty will arise: important wild areas that had been protected by the dangers of malaria will be exposed to unwise development."

A setback in eradication strategy was just preceded by the famous attack on the use of DDT on the environmental ground by Rachel Carson's, now classical, "Silent Spring" in 1962. She argued that DDT and its active metabolites DDE and DDD survive and accumulate in the body fat of animals high up in the food chain and cause devastation on the bird life.

The authors argue that though many fears surrounding DDT were unfounded and not based on proper scientific studies, it was banned by the US. Environmental Protection Agency (EPA) in 1972. This lead was accepted by the most developed countries and DDT was banned for all uses. Initially the use of DDT for public health purposes was allowed, because miniscule amount of the insecticide use would have no environmental accumulation as would happen in agricultural use; this was soon forgotten however and the ban became total. Soon major western donor agencies followed suit. As the environmental movement in the west grew in power and influence, the use of DDT and other organo chlorines like dieldrin, aldrin etc. became one of the key issues. In the 1980s "sustainable development" became a watchword. Ex. Prime Minister of Norway and the head of the UN World Commission on Environment and Development gave a powerful support to this idea in her famous report "Our Common Future."

"Sustainable development" among other things is about intergenerational justice; development that meets the needs of the present without compromising the ability of the future generation to meet their own needs. Strong interpretation of "sustainable development" implies that natural capital such as forests, wildlife etc cannot be substituted for man made capital. This is a heady stuff and the implications are far-reaching and profound.

The strong entry of environmentalist politics of the West has meant that highly effective and cheap insecticides like DDT can not be used in the fight against malaria in the less developed countries (LDCS). The threat to the LDCS is further intensified by the proposed international agreement under the United Nations Environment Programme (UNEP) to ban the use of persistent organic pollutants (POPs) known as Dirty Dozen like DDT, dieldrin, aldrin, poly chlorinated biphenyls (PCBS) etc. Tren-Bate argue convincingly that the POPs instrument will make it very easy for the developed countries to force the ban on the DDT even for malaria.

To use or not to use DDT in malaria control is no longer determined by the considerations of epidemiology - the vector characteristics and the developmental needs of the poor countries like Mozambique. WHO's Roll Back Malaria programme based on diagnosis, treatment and "environmentally safe" drug impregnated mosquito nets, to the exclusion of vector mosquitoes even in the cities is not so innocuous as it appears. In the cities, mosquitoes breed unchecked in man made structures because elementary precautions in construction and maintenance are not followed or enforced. RBM strategy that effectively excludes vector mosquitoes from its operative strategy has ensured this. Meanwhile killers like dengue fever, and falciparum malaria parasites resistant to chloroquine flourish undeterred and spread their reach in the rural areas. Urban malaria has become a major threat.

It is not a simple swing of pendulum between two schools of thought, vector Vs parasite that prevailed more than half a century ago. Tren-Bates' arguments compel one to conclude that considerations and politics of "sustainable development", with its dangerous ambiguity, if not vacuousness, that drives WHO and other major UN agencies to push relentlessly for the ineffective, and ritualistic programmes like RBM. Their elaboration of implications for poor country like Mozambique is revealing and worrying. DDT, from what they say, has still an important role in malaria control even in country like Mozambique, where it is deeply entrenched, where one would be extremely cautious to intervene on purely epidemiological considerations; but in the changed context if countries like Mozambique want to embark on the economic development, they have all the right to take such a difficult decision as the use of DDT to control malaria.

"Sustainable development" smacks of arrogance, and indifferent elitism of the rich and powerful, if not of imperialism. In countries like Mozambique and India, malaria kills millions because of such doctrinaire ideologies as "sustainable development".

Date: 20/2/01, Anil Patel

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